NASA to Launch Planet-Hunting Kepler Spacecraft Tonight

Workers attach the two-part payload fairing over the Kepler spacecraft in preparation for it March 6, 2009 launch from Cape Canaveral Air Force Station, Fla. The cover, designed to jettison shortly after launch, protects the spacecraft from the friction and turbulence as it speeds through the atmosphere during launch.Credit: NASA/Jack Pfaller

The $600
million Kepler
spacecraft is slated to blast off from Florida?s Cape Canaveral Air Force
Station tonight at 10:49 p.m. EST (0349 March 7 GMT) on a mission that could profoundly
change how humans perceive their role in the universe.

?It very
possibly could tell us that Earths are very, very common, that we have lots of
neighbors out there,? said Ed Weiler, NASA?s associate administrator for
science missions. ?Or it could tell us that Earths are really, really rare, and
we?re all alone out there.?

Named after Johannes Kepler, the 17th century German scientist who pioneered the laws
of planetary motion, the Kepler the spacecraft is NASA?s first mission
dedicated seeking out planets like Earth orbiting stars at just the right
distance to allow liquid water - a vital ingredient for life on our own world -
to exist on the surface.

?Kepler is
essentially a planet-sifter for Earths,? said Patricia Boyd, NASA?s Kepler
program scientist, adding that the mission is expected to take a census
of Earth-like planets to see how common they are in our Milky Way galaxy. ?The
answer to that question could fundamentally shift our picture of our place in
the universe.?

Astronomers
have discovered nearly 340 extrasolar planets since 1995, but most of them are
gas giants, like Jupiter, or larger.

?What we?re
really interested in are rocky planets like that of the Earth,? said William
Borucki, Kepler's principal investigator at NASA's Ames Research Center in Moffett
Field, Calif.

The
forecast for tonight?s
planned launch appears pristine, with a less than five percent chance of
foul weather thwarting Kepler?s liftoff, mission managers said. The mission
has two launch opportunities; a three-minute window at its first launch time
and another window that opens at 11:13 p.m. EST (0414 March 7 GMT).

NASA
delayed Kepler?s launch by one day last week to allow extra rocket checks on
the spacecraft?s Delta 2 booster to ensure it was fit to fly. The precaution,
stemmed from the Feb. 24 failure of a different rocket carrying a NASA
Earth-watching satellite, found Kepler?s booster in fine shape for tonight?s
planned liftoff, mission managers said.

Strange
New Earths

After
launch, Kepler is designed to turn its
unblinking camera eye at a patch of sky between 600 and 3,000 light-years
from Earth in the direction of the constellations Cygnus and Lyra. The target
zone covers an area similar to what a human hand could cover when held at arm?s
length.

Kepler will
stare at the region for at least 3 1/2 years, measuring the light from 100,000
stars every half hour with a 95 million-pixel camera to watch for the slight dip
in a star?s brightness that signals a planet moving across it as seen from
Earth. It?s the equivalent of trying to spot a flea crawl across a car
headlight from miles away, NASA has said.

?We
certainly won?t find E.T.,? Borucki said. ?But we will find E.T.?s home by
looking at all of these stars.?

But
spotting planets the size of Earth is hard work. Kepler will seek out planets
that circle their parent stars in just the right orbit, a so-called habitable
or ?Goldilocks? zone that is neither too hot nor cold for liquid water to
exist.

For example,
last month European scientists using the COROT space telescope announced the discovery
of COROT-Exo-7b, a small exoplanet with a mass that weighs in at just twice
the size of the Earth.

But while
the planet?s status as the smallest exoplanet has caused some debate,
researchers are sure the alien world orbits very close to its parent star,
making the trip once every 20 hours. Surface temperatures on COROT-Exo-7b are
estimated at 1,832 to 2,732 degrees Fahrenheit (1,000 to 1,500 degrees
Celsius).

?If that
planet has an ocean, it flows with molten lead,? said Borucki, adding that a
planet circling a star from too far out faces a different problem. ?Too far out
and they?re too cold. They?re probably frozen solid.?

So Kepler
will be hunting for planets that move across their stars, or transit, about
once every Earth year. Prime candidates will be ones the space telescope spots
three times during its initial mission, mission researchers said.

Kepler will
scout for its Earth-like quarry from an orbit that trails behind the Earth and
circles the sun once every 371 days. While the spacecraft is designed to last 3
1/2 years, it carries enough fuel for up to six years of planet hunting just in
case its mission is extended.

?We?re very
proud of the vehicle we have built,? said Jim Fanson, Kepler?s project manager
at NASA?s Jet Propulsion Laboratory in Pasadena, Calif. ?This is a crowning achievement
for NASA and a monumental step for our search for other Earths around other
stars.?

NASA
will broadcast the Kepler?s launch late Friday night live on NASA TV beginning
at 8:30 p.m. EST (0130 March 7 GMT). Click
here for SPACE.com?s live launch webcast and countdown coverage.